Abnormal arterial vasoconstriction is one of the major causes inducing post-flight orthostatic intolerance.It has been documented that Rho kinase (ROCK) could enhance the contraction of vascular smooth muscle cells.In this study, we investigated the association between changed vasoconstriction of abdominal aorta and common carotid artery induced by sinulated microgravity and ROCK.Tissue bath vas used to measure arterial vasdreactivity, western blot and immunohistochemistry were applied to observe ROCK Ⅱ expression.It was shown that (1) KCl and phenylephrine induced contraction were both decreased significantly in abdominal aorta but increased in common carotid artery by hindlimb unloading (HU), which were inhibited significantly in both vessels by ROCK specific inhibitor Y-27632.(2) ROCK Ⅱ expression was upregulated in both abdominal aorta and common carotid artery by HU.These data suggest HU-induced abnormal vasoconstriction is associated with ROCK.The aberrant upregulated ROCK Ⅱ expression in abdominal aorta induced by HU needs further clarification through detection of ROCK activity.